Controlling the morphology of polymer blends using periodic irradiation.

Morphology is the decisive factor controlling practical properties such as impact strength or transparency in multiphase polymeric materials. The co-continuous structure formed by polymers has been of great interest to material scientists because of their superiority over those with random morphology. Although a number of efforts--including forcibly freezing the spinodal structure of polymer blends--have been made to produce materials with co-continuous structures, an efficient method for controlling their regularity is still lacking. Here, we demonstrate a novel method using periodic photo-crosslinking to control the length-scale distribution of the spinodal structure in binary polymer blends. It was found that the period distribution of the resulting co-continuous structure became significantly narrow under this periodic forcing. Also, there exists a particular irradiation frequency at which the periodic structure exhibits a minimum, indicating the existence of an ordering process driven by the external modulation frequency. Our findings reveal an easy way to produce polymer materials that is not only useful for optical applications, but also promising for biological separation, such as hemodialysis.